Conventionally, in hospitals, etc., articles to be sterilized, e.g., bandages, surgical knives, forcipes, operating gowns, are usually sterilized by a sterilization method comprising the steps of: accommodating the articles in a sterilizing chamber of a sterilizer; pressurizing the sterilizing chamber by saturated steam until reaching prescribed pressure; and maintaining the pressure and temperature in the sterilizing chamber for a prescribed time.
In the case of a large-sized sterilizer capable of sterilizing a large amount of articles, saturated steam is supplied to the sterilizer from a large boiler of a hospital.
If the saturated steam supplied from the large boiler is improper for sterilization or if required capacity of saturated steam for a plurality of sterilizers is greater than capacity of the boiler, a saturated steam generator must be provided to each sterilizer.
For example, a steam sterilizer having a saturated steam generator is disclosed in Japanese Patent Gazette No. 9-285527, wherein saturated steam (pure saturated steam) generated by evaporating pure water, which has been precise-filtered or deionization-treated, is supplied into a sterilizing chamber.
The steam sterilizer disclosed in the Japanese gazette is shown in FIG. 13. In FIG. 13, a body proper 100 of the steam sterilizer comprises: an inner cylinder 104 in which a sterilizing chamber 102 for accommodating articles to be sterilized is formed; an outer cylinder 106 provided outside of the inner cylinder 104; and a jacket 108 provided between the inner cylinder 104 and the outer cylinder 106.
The steam sterilizer shown in FIG. 13 has a steam generator 110 in which pure water supplied by a water supply tube is evaporated to generate pure steam. In the steam generator 110, steam, which is used as a heat source for evaporating pure water, is generated by a large boiler, so it is supplied via a steam tube 120, a control valve 118, a jacket 108 of the steam sterilizer, and a tube 119. The steam supplied to the jacket 108 is used for heating the inner cylinder 104.
The pure steam generated by the steam generator 110 is directly supplied to the sterilizing chamber 102 of the body proper 100 via a pure steam supply tube 116, in which a control valve 114 is provided to a mid part.
The pure steam, which has sterilized the articles in the sterilizing chamber 102, is discharged via a discharge tube 122 and a tube 124, to which a control valve 126 is provided. When pressure in the sterilizing chamber 102 falls to the atmospheric pressure, the control valves 114 and 126 are closed, a water ring vacuum pump 130 is actuated, a control valve 128 of a vacuum tube 132 is opened, so that a vacuum condition is produced in the sterilizing chamber 102. The vacuum condition is produced to dry the articles, on which condensed water of the pure seam is stuck.
When the pressure of the sterilizing chamber 102 is increased to the atmospheric pressure and the sterilized articles are taken out therefrom, clean air is introduced into the sterilizing chamber 102 via a filter 134 and a tube, to which a control valve 136 is provided.
Note that, a part of sealing water of the vacuum pump 130 is lost due to evaporation caused by sucking the pure steam, but the loss is supplemented by supplying water via a tube 131.
The steam sterilizer shown in FIG. 13 employs the pure steam, which is generated by evaporating pure water, as steam for sterilization. Namely, saturated steam, which is generated in a large boiler by heating water including a water conditioning agent, is not used for sterilization, so that no water conditioning agent is stuck onto the sterilized articles.
The steps of the sterilization in the sterilizing chamber 102 of the steam sterilizer shown in FIG. 13 are shown in FIG. 14. FIG. 14 shows variation of inner pressure in the sterilizing chamber 102 with respect to time elapsed, and the steps of the steam sterilization are a conditioning step, a sterilization step, a discharge step, a dry step and a final step.
Firstly, the conditioning step is started after the sterilizing chamber 102, in which the articles to be sterilized have been accommodated, is air-tightly closed. After the vacuum pump 130 is actuated and the control valve 128 is opened so as to discharge air in the sterilizing chamber 102 and produce the vacuum condition therein, the conditioning step alternately repeats two actions: a heating action, in which the control valve 114 of the tube 116 is opened to heat the articles accommodated in the sterilizing chamber 102; and a pressure reducing action, in which the vacuum pump 130 is actuated and the control valve 128 is opened to discharge air and steam from the sterilizing chamber 102 and reduce pressure therein. The conditioning step is executed so as to securely discharge air in the articles and rise inner temperature of the articles as well as surface temperature thereof when the steam is supplied into the sterilizing chamber 102 to heat the articles.
After the articles are fully heated in the conditioning step, the control valve 114 is opened to supply saturated steam into the sterilizing chamber 102 until reaching prescribed pressure, then the pressure and temperature in the sterilizing chamber 102 are maintained for a prescribed time. With this action, bacilli stuck on the articles accommodated in the sterilizing chamber 102 can be sterilized.
Then, the pressurizing steam in the sterilizing chamber 102 is discharged by opening the control valve 126, and the dry step, in which the articles wetted in the sterilization step wilt be dried, is started.
In the dry step, the pressurizing steam has been discharged from the sterilizing chamber 102 and the pressure therein has been reduces to the atmospheric pressure, then the inner pressure of the sterilizing chamber 102 is further reduced by opening the control valve 128 (closing the control valve 126) and actuating the vacuum pump 130 so as to evaporate water stuck on the sterilized articles.
By evaporating water included in the articles, the temperature of the articles fall, so that amount of evaporation from the articles is reduced.
Therefore, the control valve 136 is opened to introduce heated clean air into the sterilizing chamber 102 so as to increase the inner pressure of the sterilizing chamber 102 to near the atmospheric pressure and rise the temperature therein, so that the water stuck on the sterilized articles can be easily evaporated. Further, the inner pressure of the sterilizing chamber 102 is reduced again so as to evaporate the water left in the heated articles.
The heating action and the pressure reducing action are alternately repeated a plurality of times so as to fully dry the articles. The reason of repeating the actions is that bacilli in the air stick onto and proliferate on the articles if the articles not sufficiently dried are taken out from the sterilizing chamber 102.
After the dry step is completed, clean air is introduced into the sterilizing chamber 102 by opening the control valve 136.
Note that, the steam is supplied to the jacket 108 during the steps via the tube 120 and the control valve 118, so that the sterilizing chamber 102 is always heated.
The steam sterilizer shown in FIG. 13 is capable of sterilizing and drying the articles.
However, in the steam sterilizer shown in FIG. 13, the steam generator 110 for evaporating pure water must be provided, and the steam generator 110 is large-sized, so that the steam generator shown in FIG. 3 must be large-sized.
Since the saturated steam, which has passed through the jacket 108 and whose temperature has fallen, is used as a heat source of the steam generator 110, satisfied temperature difference between the saturated steam as the heat source and the pure steam cannot be made. Thus, heat conduction area of the heater of the steam generator 110 must broad, so that the steam generator 110 must be large-sized.
On the other hand, if superheated steam is generated in a large boiler so as to use as the heat source of the steam generator 110, the temperature difference between the saturated steam as the heat source and the pure steam can be greater, but generating the superheated steam is not improper for the boiler because thermal efficiency of the boiler is made lower.
Further, in the case of using the superheated steam generated by the large boiler as the heat source of the steam generator 110, the steam generator 110 depends on the boiler, so load of the boiler cannot be reduced, on the contrary load of the boiler is increased.
Generally, in the dry step, heated clean air is introduced into the sterilizing chamber so as to heat the articles, whose temperature has been fallen due to evaporation under negative pressure atmosphere. Thus, clean air must be heated, a tube 138 for introducing clean air into the sterilizing chamber is wound on an outer circumferential face of the outer cylinder 106, which is heated by saturated steam supplied to the jacket 108.
However, heat conductivity of air is quite lower than that of water, so winding length of the tube 138 must be long so as to heat air until reaching prescribed temperature.
On the other hand, if the winding length of the tube 138 is long, flow resistance of air in the tube 138 is made greater, so that it is difficult to introduce prescribed amount of air into the sterilizing chamber in a short time; therefore an inner diameter of the tube 138 must be greater.
By using the heated air to heat the articles whose temperature has been fallen by evaporating water under negative pressure atmosphere in the dry step, the steam sterilizer must be complex and large-sized.
A first object of the present invention is to provide a small-sized saturated steam generator including a heat source capable of heating and evaporating stored water.
A second object of the present invention is to provide a steam sterilizer having a small-sized saturated steam generator including a heat source capable of heating and evaporating stored water.
A third object of the present invention is to provide a steam sterilizer and a steam sterilization method capable of drying an article to be sterilized in a dry step, in which the article, which has been wetted in a sterilization step, without using heated air.
In some small steam sterilizers, e.g., a desk steam sterilizer used in a laboratory or a clinic, a saturated steam generator is provided in a sterilizing chamber which acts as a pressure vessel. In such steam sterilizer, a lower part of a vessel section of the sterilizing chamber is formed as a water stering section, and steam is directly generated in the sterilizing chamber.
An example of the conventional desk steam sterilizer is shown in FIG. 15. In the desk steam sterilizer 200 shown in FIG. 15, a sterilizing chamber 212, in which articles to be sterilized are accommodated, is provided in a vessel section 211, which acts as a pressure vessel. A mount plate 213, on which the articles will be mounted, is provided in the vessel section 213, and a part of the vessel section 211 above the mount plate 213 is the sterilizing chamber 212. A part of the vessel section 211 under the mount plate 213 is a water storing section 214.
A heater 216 for heating water is provided in the water storing section 214. The heater 216 is an electric heater.
In the desk steam sterilizer 200, the heater 216 heats and evaporates water in the water storing section 214, so that the articles can be sterilized by steam, which is filled in the vessel section 211 and whose temperature, humidity and pressure are prescribed values.
Usually, electric heaters are used as heaters for heating water and air. Therefore, electric power must be applied to the heater during sterilization.
The sterilization is usually executed in the daytime, so electric charge for the sterilization executed in the daytime is greater than that executed in the night.
However, since an operator is required to run the sterilizer, the sterilization cannot be constantly executed in the night in spite of low charge.
Thus, a fourth object of the present invention is to provide a small-sized steam sterilizer, e.g., a desk steam sterilizer, capable of reducing costs.
The inventors firstly studied to achieve the first object of the first to fourth objects, they found that the first object can be achieved by employing superheated steam, which is heated in a heat storage tank disclosed in Japanese Patent Gazette No. 2000-97498, as a heat source of a steam generator for generating saturated steam, without employing steam generated by a large boiler, then they reached a first basic structure of the present invention.
Namely, the saturated steam generator for generating saturated steam by heating water with superheated steam resulting from being superheated in a heat transmission tube inserted into a heat storage tank is characterized by, the provision of a saturated steam generator tank, wherein in the heat storage tank, disposed in a heat storage section composed by having a solid heat storage material and a liquid heat storage material filled therein are the heat transmission tube and a heater, which heats the solid heat storage material and the liquid heat storage material, and it being arranged that superheated steam resulting from passing through the heat transmission tube is used as a heat source to heat stored water so as to generate saturated steam.
In the first basic structure, by filling the solid heat storage material and the liquid heat storage material in the heat storage section of the heat storage tank with high density, heat capacity stored in the heat storage section and heat conductivity can be improved. Since sufficient heat capacity can be stored in the heat storage section by the heater, the heat stored in the heat storage materials is supplied to the heat transmission tube, and the water in the heat transmission tube can be immediately formed into the superheated steam even if the heater for heating the heat storage materials is out of operation.
Further, since the superheated steam generated in the heat storage tank is used as the heat source for heating the water stored in the saturated steam generator tank, sufficient temperature difference between the superheated steam and the saturated steam can be produced, and heat transmission area of the heater for heating the water stored in the saturated steam generator tank can be smaller than that in the case of using saturated steam as a heat source, so that the saturated steam generator can be small-sized, and the saturated steam can be generated in a short time from the out of operation state.
The inventors found that load of a large boiler can be reduced by employing said saturated steam generator, and they reached the second basic structure of the present invention.
Namely, the second basic structure is a steam sterilizer having a sterilizing chamber, in which an article to be sterilized is accommodated, and a saturated steam generator, which supplies saturated steam into the sterilizing chamber, wherein the saturated steam generator comprising: a heat storage tank including a heat storage section, in which a solid heat storage material and a liquid heat storage material are filled, and in which a heater for heating the solid heat storage material and the liquid heat storage material and a heat transmission tube for blowing off superheated steam generated by superheating water supplied are provided; a saturated steam generator tank, in which stored water is heated, by the superheated steam blown off from the heat transmission tube as a heat source, so as to generate saturated steam; and a steam supply tube supplying the saturated steam generated in the saturated steam generator tank into the sterilizing chamber.
In the saturated steam generator of the steam sterilizer of the second basic structure, by filling the solid heat storage material and the liquid heat storage material in the heat storage section of the heat storage tank with high density, heat capacity stored in the heat storage section and heat conductivity can be improved. Since sufficient heat capacity can be stored in the heat storage section by the heater, the heat stored in the heat storage materials is supplied to the heat transmission tube, and the water in the heat transmission tube can be immediately formed into the superheated steam even if the heater for heating the heat storage materials is out of operation.
Further, since the superheated steam generated in the heat storage tank is used as the heat source for heating the water stored in the saturated steam generator tank, sufficient temperature difference between the superheated steam and the saturated steam can be produced, and heat transmission area of the heater for heating the water stored in the saturated steam generator tank can be smaller than that in the case of using saturated steam as a heat source, so that the saturated steam generator can be small-sized, and the saturated steam can be generated in a short time from the out of operation state.
As described above, the steam sterilizer of the second basic structure has the saturated steam generator which is small-sized and capable of generating saturated steam in a short time from the out of operation state, so the steam sterilizer can be small-sized and capable of operating with independent cycles.
In the first and the second basic structures, if the solid heat storage material filled in the heat storage section includes solid heat storage grains having different diameters, each of the solid heat storage grains having short grain diameters is provided between the solid heat storage grains having large diameters and gaps between the heat storage grains are filled with the liquid heat storage material, density of the both heat storage materials in the heat storage section can be greater and heat capacity stored in the heat storage section can be greater, too.
Preferably, the solid heat storage material may include grains made of one or more selected from magnesia, magnetite, silica and alumina, and the liquid heat storage material may be a nitrate.
The heater for heating the solid heat storage material and the liquid heat storage material may be an electric heater so that heat can be stored in the heat storage materials by low cost midnight electric power, therefore clean and inexpensive saturated steam can be gained.
Further, if the saturated steam generator further comprise: a water supply tank for supplying water to the saturated steam generator tank; and a drain tube connecting the saturated steam generator tank to the water supply tank so as to use drain of the superheated steam, which is used in the saturated steam generator tank as the heat source, as a heat source for heating the water in the water supply tank, the heated water can be supplied to the saturated steam generator tank, so that further inexpensive saturated steam can be gained.
If the saturated steam generator tank comprises: an evaporation tank in which the stored water is heated and saturated steam is generated by a heater whose heat source is superheated steam supplied from the heat storage tank; and a level detection tank which is communicated to the evaporation tank and which includes means for detecting level of the water stored in the evaporation tank, the water level in the evaporation tank can be easily controlled.
If the saturated steam generator further comprises means for removing drain from saturated steam generated in the saturated steam generator tank, the saturated steam including no drain can be gained.
If a body proper of the sterilizing chamber includes: an inner cylinder in which the article to be sterilized is accommodated; an outer cylinder, which is provided outside of the inner cylinder; and a jacket which is provided between the inner cylinder and the outer cylinder and to which steam for heating the sterilizing chamber is supplied, and wherein the saturated steam generated in the saturated steam generator is directly supplied into the sterilizing chamber, different kinds of proper steam can be respectively supplied to the sterilizing chamber and the jacket according to purposes.
The inventors studied to achieve the third object of the present invention, they found that water is evaporated from the article and temperature of the article is fallen in a dry step for drying the article which has been wetted in a sterilization step, but temperature of the article can be risen without substantially wetting the article, in the dry step, by using the superheated steam instead of heated air, so that they reached a third basic structure.
Namely, the third basic structure is a steam sterilizer having a sterilizing chamber, which is provided in a body proper and in which an article to be sterilized is sterilized by saturated steam and the article, on which condensed water of the saturated steam is stuck, is dried, comprising: means for reducing pressure in the sterilizing chamber and evaporating the water stuck on the article; means for blowing the superheated steam into the sterilizing chamber, whose pressure has been reduced, so as to rise temperature of the article, whose temperature has been fallen by evaporating the water by pressure reduction; a control section alternately actuating the pressure reducing means and the blowing means so as to dry the article; and means for supplying the superheated steam, which has a heat storage tank including a heat storage section, in which a solid heat storage material and a liquid heat storage are filled, and in which a heater for heating the solid heat storage material and the liquid heat storage material and a heat transmission tube for blowing off superheated steam generated by superheating water supplied are provided.
Further, the method related to the third object is a steam sterilization method comprising the steps of: sterilizing an article to be sterilized, which is accommodated in a sterilizing chamber of a body proper of a sterilizer, by introducing saturated steam into the sterilizing chamber; reducing pressure in the sterilizing chamber so as to evaporate condensed water stuck on the article; blowing a heated fluid into the sterilizing chamber so as to rise temperature of the article, whose temperature has been fallen by evaporating the water stuck thereon, so as to rise the temperature of the article; and alternately repeating the reducing step and the blowing step so as to dry the article, wherein the heated fluid blown into the sterilizing chamber is superheated steam, and the superheated steam is supplied by using a heat storage tank having a heat storage section, in which a solid heat storage material and a liquid heat storage material are filled and in which a heater for heating the solid heat storage material and the liquid heat storage material and a heat transmission tube for blowing off superheated steam generated by superheating water supplied are provided.
In the third basic structure, heat capacity of the superheated steam supplied from the heat storage tank is much greater than that of heated air, and amount of water of the superheated steam is less than that of saturated steam of same pressure. As described as the third basic structure, in the dry step in which the article wetted by condensed water of the saturated steam is dried after the article is sterilized by the saturated steam, the temperature of the article can be risen without wetting the article by the superheated steam, even if the superheated steam is introduced into the sterilizing chamber so as to heat the article, from which water is evaporated and whose temperature is fallen under a pressure reducing atmosphere.
As described above, in the third basic structure, no heated air is introduced into the sterilizing chamber so as to heat the article whose temperature has fallen, so no heater for heating air is required.
In the third basic structure, if the body proper of the steam sterilizer is a single-wall pressure vessel, in which the sterilizing chamber is provided, the structure of the sterilizer can be simplified.
Further, the inventors studied to achieve the fourth object and found that costs of a small-sized steam sterilizer, e.g., a desk steam sterilizer, can be reduced by storing heat generated by midnight electric power in a heat storage tank even if the sterilizer is operated in the daytime, so that the inventors reached the fourth basic structure.
Namely, the fourth basic structure is a steam sterilizer comprising: a vessel, which is a pressure vessel and in which a sterilizing chamber for sterilizing an article to be sterilized accommodated therein and a water storing section are provided; and means for heating water stored in the water storing section to generate steam in the vessel, wherein the heating means includes: a heat storage tank, in which a heat storage section filled with a solid heat storage material and a liquid heat storage material, a heater for heating the heat storage section, and a heat transmission tube passing through the heat storage section so as to heat water in the heat storage section and blow off superheated steam are provided; and a superheated steam supply tube connected to the heat transmission tube so as to pass the superheated steam, which is generated in the heat storage section, through the water storing section.
In the fourth basic structure, preferably the solid heat storage material includes grains made of one or more selected from magnesia, magnetite, silica and alumina, and/or the liquid heat storage material is a nitrate.